There is this article in the wordpress website that counts:
- words: 8207
- characters: 56302
- estimated reading time: 43m
- 20 images
and 183 paragraphs and 201 blocks.
Could affect loading time of every page, including the wp-admin?
Wordpress depends more on the efficiency of the code that queries the database, and the templates in the theme that display the pages. And external requests (off site) And large images. And more.
The best way to find slowness is via the Developer tools in your browser (usually via F9). The Network tab will show you the timings on all of the requests for a page. You can then look for slow request responses.
To check your theme's efficiency with database queries, use the "Query Monitor" plugin. Lots of good info found by that plugin.